1. Field of the Invention
This invention relates to a well completion apparatus and to methods for its use. More particularly, this invention relates to providing communication between the interior and exterior of a conduit disposed in a well bore penetrating production strata of a subterranean formation.
2. Description of the Prior Art
In most well bores, there are zones of strata in the formation through which the bore hole passes which should not be in communication with the well bore. These strata are excluded from communication with the well bore with a casing, liner, or tubing. By "casing" is meant a conduit of slightly smaller external diameter than the internal diameter of the bore hole and extends from the earth's surface to or beyond the producing strata. By "liner" is meant a conduit of smaller external diameter than the internal diameter of the casing to be disposed inside the casing but do not extend up to the earth surface. By "tubing" is meant a conduit usually of smaller external diameter than the internal diameter of the casing, in some cases smaller than the internal diameter of the liner to be disposed inside the well bore, casing or liner, extending from the earth's surface to any point below the earth's surface. Hereinafter, conduits refer to casings, liners or tubing. These conduits are disposed in the well bore and sometimes cemented in the well bore, i.e., the cement fills portions of the annular space between the well bore and the conduit to seal off the well bore above and/or below the production strata. Well bores which are intended for solution mining of metal salts, e.g., NaCl, KCl, etc., need not be cemented to seal the producing strata from that which overlies or underlies the strata because the liquid solvents used can be insulated from the roof and the floor of the cavity by light and heavy immiscible liquids and solids. After disposing the conduits in the well bore and whether cementing is done or not, communication between the conduits and the producing zone must be established.
The prior art has offered various methods for establishing communication between the conduit and the producing zone. Communication is made by such methods as removing a drill bit from the end of a drill pipe after drilling a well bore, thereby opening the end of the drill pipe. Subsequently, the drill pipe remains in the well bore to serve as a conduit because the cost of withdrawing a string of drill pipe can be just as expensive as the high cost of drilling. But, the removal of the drill bit is done commonly by explosives. This method is unsatisfactory due to the failure of ignited material to explode or due to damage of the subterranean formation because of shock waves that crack the cement or loosen rock strata. Loosened cement and rock clog the conduits or damage pumping machinery when debris is produced with the production fluid. The danger of explosives causing shock waves to collapse the roof of a solution mined cavity is even greater than in oil bearing sands and rock because of the greater amount of supporting material removed during most solution mining processes. Therefore, the use of explosives in solution mines is even more unsatisfactory because of the greater risk posed.
Another method of establishing communication between a conduit and a producing zone is by creating a passageway through protruding ports on the wall of a conduit or through the wall of the conduit itself. Passageways are made by perforating the conduit by the use of explosives, directing projectiles against a casing wall as taught by U.S. Pat. No. 2,876,843. This method is unsatisfactory for the reasons given above as well as due to the failure of the projectile to penetrate the conduit and/or the cement.
Many methods create passageways without the use of explosives such as by utilizing acid to attack a plug disposed in a port in the wall of a casing as taught by U.S. Pat. No. 3,312,280. This method also has its shortcomings, since extreme care must be taken so the acid does not attack the cement between the casing and the well bore, thereby weakening the sealing bond. Moreover, acid solutions may contaminate salt solutions desired to be produced. Also, once a small hole is created in an attacked section of the casing, the remaining acid may leak away before creating a large enough hole for production fluid to flow adequately through the casing wall.
U.S. Pat. No. 3,076,507 teaches the use of incendiary chemical fluids contained by an apparatus which directs the incendiary fluid against a certain area of a conduit, thereby creating a passageway through the conduit wall. This method can be extremely dangerous since some of the fluids utilized are volatile and difficult to keep under control. Inadvertent release of the fluid can be catastrophic. The extra expense of using treating fluids, as well as pre-ignitors in conjunction with the incendiary chemical fluids may also be required. The undesirability of using this method is self evident.
U.S. Pat. No. 3,360,047 teaches the use of displaceable plugs which are displaced by fluid pressure from the wall of a casing. When fluid pressure is applied to the casing, the plugs will be displaced leaving a passageway. This method is undesirable because it requires a source of fluid pressure at the well site, and there is an additional burden of having to make sure that all the joints in the casing and all connections are sufficiently tight so that enough fluid pressure can be developed to blow out or displace the plugs.
U.S. Pat. No. 3,057,405 teaches the use of ports which extend out of a section of the conduit, through which a passage is provided. A material which melts at a temperature close to the bottom hole temperature is disposed at the outer end of the passages. The bottom hole temperature is lowered previously by circulation of a cooling fluid through a string of tubing or drill pipe. The conduit string is then run into the well. The slowly warming up of the formation supplies the heat to melt the plugs thereby opening the passages. This method is very cumbersome in having to introduce a circulation conduit into the well. There is an additional problem of the plugs being removed prematurely if the conduit is thrust inadvertently against a hard object such as a rock protruding in the well bore. Also, unexpected high formation temperatures can cause premature melting of the plugs.
In conjunction with the shortcomings described, the prior art often require expensive equipment in order to affect communication between the conduit and the producing strata. Thus, these methods are also economically unattractive.